The cabinet
The cabinet should be extremely rigid and should not generate any resonance
(unlike e.g. a violin). Suitable is particle board of 19 or 21 mm, that can
be bought in most hardware stores. They even cut the boards to the required
sizes (down to mm). For a first attempt in building a loudspeaker cabinet,
building instructions of a kit should be used. The particle boards should
be glued or screwed together, if required both. The cabinet has to be completely
sealed.

Afterwards openings for the drivers, the terminal plate and a possible bass
reflex port have to be cut out. For drawing a pair of composes should be used,
the holes should be cut with a compass saw.

The drivers
The drivers convert electrical signals - coming from the amplifier - into
mechanical waves that are audible as sound. Usually more than just one driver
is needed for ensuring that the entire audible frequency range is represented.
Low frequencies require large diameter diaphragm cones (short: diaphragms
or cones), high frequencies require small diameter cones. Sometimes there
is even a third driver with a medium diameter handling midrange frequencies.

The crossover
The purpose of the crossover is to divide and distribute frequency ranges
to the individual drivers according to the their frequency capabilities. The
high frequency driver (called: tweeter) cannot handle high power, low frequency
sound while the low frequency driver (called: bass driver) cannot handle high
frequencies.

The components of the crossover

The crossover receives electrical signals from the terminal. The terminal
consists of (usually) two binding posts to which the two cables - coming from
the amplifier - are connected.

The drivers receive the electrical signal from the crossover, usually by
means of two cables. In the picture to the left the two circles represent
the two terminals.

Coils, representing a pass through for low frequencies and an interruption
of high frequencies.

Capacitors, representing a pass through for high frequencies and an interruption
of low frequencies.

The picture below shows the crossover of the PA 250 kit as an example:
The characteristics of each component are described by its corresponding value.

The two circles left on the picture symbolize the two terminals for the
connection to the amplifier.

The bass driver receives signals via a coil with 0.39 uH. Additionally,
there are a 3.9 uF MKT capacitor and a 3.3 Ohm resistor in parallel to the
bass driver. These both components in conjunction with the coil achieve
that almost no high frequencies reach the bass driver.

Branching off to the right is a 5.6 uF capacitor, a pass through for
high frequencies only. An additional 0.22 mH coil acts like a short circuit
for low frequencies ensuring that only high frequencies are fed through.

Continuing horizontally a thermistor Si 0.5A is employed, interrupting
the signal to the tweeter should it become too hot. This type of protection
is required for speakers being used at parties where the volume is turned-up
frequently. (Damage to the drivers occurs mostly after the sound quality
has already deteriorated dramatically - a condition most DJ don't care about.)

Since a tweeter possesses a high efficiency, a resistive divider needs
to be installed reduce the overall volume. The capacitor prevents low frequencies
from reaching the Peerless PHH 25 tweeter.

The crossover described here is very simple and is taken from our PA 250 kit.
It is e.g. used by a Swiss youth group for indoor and outdoor sound reproduction.
At 250 Watt input this speaker achieves a sound pressure level of 120 dB (1
metre), almost exceeding the pain threshold. - This speaker is tuned for maximum
sound level and can withstand short peaks of up to 1000 Watt.